The role of molluscan hemolymp cells as internal defense mechanisms is being studied. Specifically, the mechanisms by which foreign microorganisms and/or macromolecules are phagocytized and degraded intracellularly are being investigated by the use of electron microscopy and biochemistry. The objective is to ascertain the optimal operative parameters of these enzymes and their kinetic properties so that shellfish in the process of being cleansed can be maintained in defined conditions conducive to the essential activities of these intracellular enzymes. In addition, hematopoetic tissues of molluscs are being cultured in vitro so that the mechanisms involved in the production of phagocytic granulocytes can be studied. Our studies have been limited primarily to three species of molluscs that are of economic importance: The American oyster, Crassostrea virginica; the quahaug clam, Mercenaria mercenaria; and the soft-shelled clam, Mya arenaria.